Combined Imaging Techniques Best at Finding Bone Metastases

Fran Lowry

June 28, 2012

June 28, 2012 (Miami Beach, Florida) — Combining 2 imaging agents in a single positron emission tomography/computed tomography (PET/CT) scan is feasible and yields comparable information to that obtained with each individual scan, and it may even be more cost-effective, researchers said here at the SNM 2012 Annual Meeting.

Dr. Andrei Iagaru

"The simultaneous administration of F-18 NaF and [fluorine-18 fluorodeoxyglucose (F-18 FDG)] imaging agents in a single PET/CT scan has the potential to improve diagnostic accuracy and patient convenience," lead investigator Andrei Iagaru, MD, from Stanford University in California, told Medscape Medical News.

"Importantly, when you combine the 2, you don't lose any of the diagnostic information," he added.

Dr. Iagaru and colleagues compared the use of PET involving both F-18 NaF, a sodium fluoride probe with affinity for bone, and F-18 FDG, a probe that acts like glucose and reflects cells' use of energy, with CT alone in the detection of bone metastases.

The researchers retrospectively reviewed 51 patients with a variety of biopsy-proven cancers who underwent separate NaF PET/CT and FDG PET/CT scans and combined NaF/FDG PET/CT scans (3 scans per patient). There were 39 men and 12 women. The age range was 19 to 84 years (average age, 53.9 ± 16.2 years).

The 3 scans were performed within a 2-week period for each patient, and the results were compared for the detection of bone metastases.

Results showed that the composite NaF and FDG PET/CT images identified more bone metastases than the individual scans alone, as well as more than CT scans alone.

For CT alone, the sensitivity was 0.59, the specificity was 0.76, the positive predictive value (PPV) was 0.65, and the negative predictive value (NPV) was 0.71.

For 18F FDG PET/CT, the sensitivity was 0.64, the specificity was 0.97, the PPV was 0.93, and the NPV was 0.78.

For 18F NaF, the sensitivity was 0.91, the specificity was 0.90, the PPV was 0.87, and the NPV was 0.93.

For combined 18F NaF/18F FDG, the sensitivity was 0.96, the specificity was 0.90, the PPV was 0.88, and the NPV was 0.96.

"To us, this is proof of the noninferiority of doing the combined approach, and we truly believe that the sum is better than the parts. It adds more diagnostic value," Dr. Iagaru said.

"The main advantage is that the patient can have both studies done and only have to come in to the center once, and there may also be some cost savings with this approach as well," he said.

Dr. Norman LaFrance

Commenting on this study for Medscape Medical News, Norman LaFrance, MD, an imaging consultant in Leesburg, Virginia, said the findings are what one would expect.

'The big question is, How does this change patient management?" he said. "Two of the most common cancers — breast and prostate — go to the bone. There are some immunotherapies that require documented and diagnosed bony disease. If using the combination of studies together helps to discover bony metastases earlier than with a bone scan alone, this might allow the patient to get some effective therapy earlier, and this would definitely be a good thing."

Dr. Iagaru and Dr. La France have disclosed no relevant financial relationships.

SNM 2012 Annual Meeting: Abstract 586. Presented June 11, 2012.

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